Permeation of various liquids and gases through plastic films, pipes, or containers can be a problem in some circumstances (e.g., permeation of water vapor through food or pharmaceutical packages) for particular uses. For example, the pharmaceutical industry has developed complex dosage forms that may be susceptible to degradation upon prolonged exposure to moisture. Currently, a number of approaches are available to address the problem of packaging material permeability. Many of these approaches, however, require high cost materials and/or increased manufacturing complexity, and/or the use of toxic or corrosive reagents to achieve the goal of permeability reduction.
In one approach, reduction of the permeability of a packaging material is achieved through a chemical surface treatment (e.g., oxidation with fluorine or sulfur trioxide). For example, polyalkylene containers are sometimes treated with gaseous fluorine to inhibit permeation of gasoline, pesticide, or herbicide products from the containers. U.S. Pat. No. 3,862,284 discloses a process of modifying surface properties of blow-molded thermoplastic articles using a blowing gas which contains fluorine. British Patent No. 2,069,870 discloses a process for reducing permeability of a surface of a container by treating the surface of the container with sulfur trioxide, washing with an aqueous medium, and applying a layer of a dispersion of a melamine-formaldehyde or urea-formaldehyde condensation product. While the chemical surface treatment can provide the treated material with requisite barrier properties, this approach can also be costly to implement, particularly, on large scale, because of the need for aggressive, toxic chemicals (e.g., fluorine or sulfur trioxide), which require special handling and specialized non-corroding equipment.
In another approach, reduction of the permeability of a packaging material is achieved through the use of multilayer films in which each layer has a dedicated function. For example, U.S. Pat. No. 4,515,836 discloses a process for coating a substrate, such as poly(ethylene terephthalate), with a gas barrier coating of a copolymer of vinylidene chloride and small amounts of another co-monomer, such as acrylates or acrylonitrile. Current many pharmaceutical blister packages are often prepared from such multilayer films (e.g., PVC/PE/PVdC, PVC/PCTFE/PVC, PVC/EVOH/PCTFE, and PVC/PE/PCTFE). However, the need for each additional layer in a film leads to an increase (1) in packaging weight, (2) manufacturing complexity, (3) and material expenditure, thereby driving the end consumer costs higher.
There remains a need for inexpensive and easy to manufacture on large scale packaging materials having a barrier film, particularly, for food and pharmaceutical packaging. Thus, the present invention addresses the problem of reducing packaging material permeability without the disadvantages of the approaches outlined above.